There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

Fabrication techniques developed for graphene research allow the disassembly of many layered crystals (so-called van der Waals materials) into individual atomic planes and their reassembly into designer heterostructures, which reveal new properties and phenomena. Andre Geim and Irina Grigorieva offer a forward-looking review of the potential of layering two-dimensional materials into novel heterostructures held together by weak van der Waals interactions. Dozens of these one-atom- or one-molecule-thick crystals are known. Graphene has already been well studied but others, such as monolayers of hexagonal boron nitride, MoS2, WSe2, graphane, fluorographene, mica and silicene are attracting increasing interest. There are many other monolayers yet to be examined of course, and the possibility of combining graphene with other crystals adds even further options, offering exciting new opportunities for scientific exploration and technological innovation. Research on graphene and other two-dimensional atomic crystals is intense and is likely to remain one of the leading topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. The first, already remarkably complex, such heterostructures (often referred to as ‘van der Waals’) have recently been fabricated and investigated, revealing unusual properties and new phenomena. Here we review this emerging research area and identify possible future directions. With steady improvement in fabrication techniques and using graphene’s springboard, van der Waals heterostructures should develop into a large field of their own.

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Van der Waals heterostructures

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Ultra-dielectrophoretic force spectroscopy array for probing intermolecular affinities

Letter pubs.acs.org/NanoLett Artiﬁcial Photosynthesis on TiO 2 ‑Passivated InP Nanopillars Jing Qiu, ‡ Guangtong Zeng, † Mai-Anh Ha, ∥ Mingyuan Ge, † Yongjing Lin, ⊥ Mark Hettick, ⊥ Bingya Hou, § Anastassia N. Alexandrova, ∥,⊥ Ali Javey, # and Stephen B. Cronin* ,†,§ Department of Chemistry, ‡ Department of Materials Science, and § Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States Department of Chemistry and Biochemistry, ⊥ California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90025, United States Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States S Supporting Information ABSTRACT: Here, we report photocatalytic CO 2 reduction with water to produce methanol using TiO 2 -passivated InP nanopillar photocathodes under 532 nm wavelength illumination. In addition to providing a stable photocatalytic surface, the TiO 2 -passivation layer provides substantial enhancement in the photoconversion eﬃciency through the introduction of O vacancies associated with the nonstoichiometric growth of TiO 2 by atomic layer deposition. Plane wave-density functional theory (PW-DFT) calculations conﬁrm the role of oxygen vacancies in the TiO 2 surface, which serve as catalytically active sites in the CO 2 reduction process. PW-DFT shows that CO 2 binds stably to these oxygen vacancies and CO 2 gains an electron (−0.897e) spontaneously from the TiO 2 support. This calculation indicates that the O vacancies provide active sites for CO 2 absorption, and no overpotential is required to form the CO 2 − intermediate. The TiO 2 ﬁlm increases the Faraday eﬃciency of methanol production by 5.7× to 4.79% under an applied potential of −0.6 V vs NHE, which is 1.3 V below the E o (CO 2 /CO 2 − ) = −1.9 eV standard redox potential. Copper nanoparticles deposited on the TiO 2 act as a cocatalyst and further improve the selectivity and yield of methanol production by up to 8-fold with a Faraday eﬃciency of 8.7%. KEYWORDS: Photoelectrochemical, InP, copper, CO 2 reduction, TiO 2 -passivation, methanol CO 2 − intermediate is so high, a cocatalyst is usually added to lower the energy barrier of this intermediate species. Lastly, the surface recombination rate of the photon-induced electron hole pairs should be as low as possible. InP is a promising material for CO 2 reduction since its band gap of 1.34 eV is well-matched to the solar spectrum. Furthermore, the surface-recombination velocity of untreated InP is low (ca. 10 4 cm/s for n-type and 10 5 cm/s for p-type). 7 Nanotexturing of InP can further enhance the photon-to-chemical energy conversion eﬃciency due to the increase in surface area and reduced reﬂection. 8 CO 2 reduction to methanol on p-InP has been reported at relatively high applied potentials of −1.3 V (vs SCE) and with low Faraday eﬃciencies (around 1%). 3 Both the poor selectivity for methanol production with respect to H 2 and severe photo- W ith the rising level of CO 2 in the earth’s atmosphere, artiﬁcial photosynthesis (i.e., a process that utilizes sunlight to convert water and carbon dioxide into carbohy- drates) has begun to receive increasing attention by researchers around the world. In 1978, Halmann et al. reported the ﬁrst photocatalytic reduction of CO 2 to hydrocarbons, including formic acid, formaldehyde, and methanol. This pioneering work utilized p-type GaP under 365 nm wavelength illumination with an applied overpotential of −1.4 V (vs SCE). 1 Many attempts have since been made to reduce CO 2 to hydrocarbons under UV illumination. 2−4 However, few researchers have achieved photoreduction under visible illumination due to the limited selection of materials. 5 For optimum solar utilization, the band gap of the semiconductor should lie in the range of 1.2−1.4 eV, as derived in the Schokley−Quiesser limit. 6 Also, the position of the conduction band (i.e., electron aﬃnity) must be as close as possible to the CO 2 to CO 2 − redox potential (−1.9 V vs NHE) in order to minimize the applied overpotential required to drive this reaction. 7 Since the energy needed to reach the © 2015 American Chemical Society Received: June 24, 2015 Revised: July 30, 2015 Published: August 12, 2015 DOI: 10.1021/acs.nanolett.5b02511 Nano Lett. 2015, 15, 6177−6181

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Correction to Artificial Photosynthesis on TiO2-Passivated InP Nanopillars

Conventional doping of crystalline Si via ion implantation results in a stochastic distribution of doped regions in the x-y plane along with relatively poor control over penetration depth of dopant atoms As the gate dimensions get to 10 nm, the related device parameters also need to be scaled down to maintain electrical activity Thus highly doped abrupt, ultra-shallow junctions are imperative for source-drain contacts to realize sub-10 nm transistors Uniform ultra-shallow junctions can be achieved via monolayer doping, wherein thermal diffusion of a self-limiting monolayer of dopant atomcontaining organic on Si surface yields sub-5 nm junctions We have extended the use of organic dopant molecules in the monolayer doping technique to introduce a new class of spin-on polymer dopants In effect, these new spin-on dopants offer a hybrid between the monolayer doping technique and traditional inorganic spin-on dopants We have been able to uniformly introduce p- and n-type dopants with doping efficiencies comparable to the monolayer doping technique Control over junction depth can be easily achieved via optimizing annealing temperature and time Concurrently, sequestering the dopant precursors within the cores of block copolymer micelles allows us to achieve precise control over the spatial positions of dopant atoms in all three dimensions owing to the high periodicity of block copolymer domains on the 10-100 nm length scale

Ordered polymer-based spin-on dopants

This paper reports the innovative use of a highly tunable material, metal-organic frameworks (MOFs), for chemical sensing on an ultra-low-power platform based on a field-effect transistor. We demonstrate proof-of-principle devices functionalized with two MOFs: "HKUST-1" for humidity sensing and "ZIF-8" for reversible NO 2 detection. These devices show minimal drift, yield highly reproducible responses, recover rapidly, and have excellent selectivity. Through this approach, devices with minimal power draw and high selectivity could be widely distributed for continuous environmental and safety monitoring.

Scalable Ultra Low-Power Chemical Sensing with Metal-Organic Frameworks

Nanosized materials, especially nanowires, have unique optical properties[1] and have been widely investigated as important building blocks for energy harvesting applications such as solar cells.[2] However, due to the large surface-to-volume ratio, recombination of charge carriers through the surface states of nanowires has been found to reduce the carrier diffusion lengths in nanowires a few orders of magnitude[3], often resulting in low efficiency.[4] Reducing the recombination by surface passivation is crucial to develop high performance nanosized optoelectronic devices, but remains largely unexplored.[5] Here we show that a thin layer of amorphous silicon (a-Si) coated on a single-crystalline silicon nanowire (sc-SiNW), forming a core-shell structure in-situ in the vapor-liquid-solid (VLS) process, reduces the density of surface states nearly 2 orders of magnitude and thereby increases the minority carrier lifetime ∼100 times. We found that individual core-shell nanowire devices have a strongly enhanced sensitivity to modulated light, compared to nanowire without shells, mainly due to surface passivation effects.

Ali Javey

Papers

Ultra-dielectrophoretic force spectroscopy array for probing intermolecular affinities

Correction to Artificial Photosynthesis on TiO2-Passivated InP Nanopillars

Ordered polymer-based spin-on dopants

Scalable Ultra Low-Power Chemical Sensing with Metal-Organic Frameworks

Strongly enhanced minority lifetimes in single silicon nanowires by surface passivation